1. Field of the Invention
This invention relates to a process for the production of polyurethanes using substituted triamino(imino)phosphoranes as catalysts. These catalysts may be used as a substitute for, or in combination with, urethane catalysts known per se, for example for the production of rigid or flexible polyurethane foams and many other polyurethane products. In the context of the invention, polyurethane products are understood to be any reaction products of polyisocyanates of compounds containing at least two isocyanate-reactive hydrogen atoms, i.e., the term polyurethane as used in the present context is understood to encompass, for example, pure polyurethanes, polyurethane polyureas or pure polyureas.
2. Description of the Prior Art
The rate of reaction between isocyanate groups and compounds containing NCO-reactive hydrogen atoms is influenced not only by the temperature of the starting products and their structure, but more importantly by suitable catalysts. In practice, bases (for example tertiary amines such as triethyl amine) are predominantly used as nucleophilic catalysts while organometallic compounds (for example Sn carboxylates such as Sn(III) octoate) are predominantly used as electrophilic catalysts. The combined use of Lewis acids and Lewis bases, which is normally characterized by synergistic effects, is known. However, it is also known that, in many applications, amines are solely used as catalysts.
Of the large number of known amine catalysts (cf. Kunststoff-Handbuch, Vol. VII, Polyurethane, Hansen-Verlag, Munchen, 1983, pages 92-98), relatively few have previously been adopted for wide scale use in practice. Those which have include 1,4-diazabicyclo[2.2.2]-octane (DABCO), bis-(2-dimethylaminoethyl)-ether, triethyl amine, dimethyl cyclohexyl amine, dimethyl ethanolamine, dimethyl benzyl amine, methyl morpholine and ethyl morpholine to name the most important. Catalysts distinguished by high activity, economic production and broad spectrum application are of course used above all. Another aspect gaining in importance is the toxicological evaluation of the catalysts in regard to processing safety and odor emission. Many of the amine catalysts used today, including DABCO and triethyl amine, are unsatisfactory due to their high volatility and their relatively strong amine odor which is transmitted to the end product produced therefrom. In view of the many potential applications of polyurethane plastics, it is equally desirable to provide catalysts "custom-made" to suit particular requirements. One possibility is to chemically modify a given type of catalyst to adapt its activity to the particular application envisaged.
Another class of compounds suitable as basic polyurethane catalysts are the bicyclic amidines described in DE-OS 1,745,418 which are comparable in activity with the strongest of the previously known amine bases and which also have a considerably weaker odor. However, a serious disadvantage of these compounds which has previously restricted their application lies in their poor hydrolysis stability which, in view of the frequent use of water as a blowing agent or chain extender in polyurethane systems, largely precludes their use because the corresponding formulations are not stable in storage.
It has now surprisingly been found that certain triamino(imino)phosphoranes may be used with advantage as catalysts for the production of polyurethanes and also polyepoxide resins.
The compounds to be used in accordance with the invention show high stability to hydrolysis and, thus, are not sensitive to atmospheric moisture or water. In addition, they show even higher catalytic activity when compared to the bicyclic amidine bases mentioned above. Another welcome effect of the catalysts proposed in accordance with the invention is that, in contrast for example to DABCO which may not be chemically altered under economically reasonable conditions, the activity of the products can be "tailored" by the choice of suitable substituents at the nitrogen. Further advantages of the compounds are their weak odor and their low volatility which leads to a distinct reduction in odor emission during the production of polyurethane products.
Further advantages include ease of handling (because the triamino(imino)phosphoranes used are liquid), good hardening behavior and also the very simple production of some of the compounds.